1. Technical Field
The present disclosure generally relates to an energy storage device and, more particularly, to an energy storage device with short response time and a control method thereof.
2. Description of Related Art
With the development of technology, portable electronic devices, such as mobile phones, tablet computers, music players, media players and the like using universal serial bus (USB) interfaces, have become indispensable in our daily life.
Since portable electronic devices consume electricity very much, the users may bring an energy storage device (for example, a mobile power bank) to charge the portable electronic devices. The energy storage device is usually compatible with the On-The-Go (OTG) standard. In other words, the energy storage device may be a peripheral powered by other devices such as a desktop computer, or a host device capable of charging an electronic device connected thereto. Moreover, in recent years, an energy storage device has been developed to charge an electronic device connected thereto, while being charged by the utility at the same time.
Furthermore, the energy storage device includes a buck circuit and a boost circuit. When the energy storage device is to charge a battery therein, the energy storage device switches to the buck circuit so as to level down the utility voltage to an adequate voltage. On the other hand, when the energy storage device is to charge an electronic device, the energy storage device switches to the boost circuit so as to level up the voltage provided by the battery to another adequate voltage. In other words, the conventional energy storage device uses a buck circuit and a boost circuit to achieve the function.
Operation principles of the conventional energy storage device are described as follows, for example. Upon receiving the utility, an adapter in the conventional energy storage device provides a maximal current of 1 A. However, the charging current of an electronic device is 1.5 A. In other words, the adapter cannot supply the electronic device. Meanwhile, the energy storage device switches to the boost circuit so that the battery provides the electronic device with energy to meet the requirement of the electronic device. In brief, in addition to the maximal current of 1 A from the adapter, the battery provides a current of 0.5 A so that the electronic device receives a total current of 1.5 A.
However, the conventional energy storage device has a few drawbacks. One is that the battery can only provide a fixed current. For example, as the load of the electronic device decreases, the electronic device only requires a current of 1.2 A. Meanwhile, the battery still provides the electronic device with a fixed current of 0.5 A, so that the adapter only provides the electronic device with a current of 0.7 A. Since the output current of the adapter becomes smaller, a controller of the conventional energy storage device determines that the adapter can meet the requirements of the electronic device and thus turns off the boost circuit and switches back to the buck circuit to charge the battery. In fact, the adapter cannot provide the electronic device with sufficient energy, and thus the conventional energy storage device switches again to the boost circuit so that the battery outputs energy. In brief, the conventional energy storage device switches between the boost circuit and the buck circuit, which causes instability of the conventional energy storage device, and fails to provide the electronic device with energy.
Moreover, another drawback of the conventional energy storage device is longer response time. It takes time for the conventional energy storage device to generate a control signal based on the present conditions to control the switching between the buck circuit and the boost circuit. In other words, the time for the conventional energy storage device to generate the control signal causes the conventional energy storage device to fail to respond to the request of the electronic device in real time, which increases the response time.